Bipolar surgical snare instruments for removing protruding tissue, such as tonsils, polyps and the like, are well known. For example, U.S. Pat. Nos. 4,493,320, 5,026,371 and 5,078,716 each describe a bipolar snare instrument that includes a pair of opposing flexible electrically conducting uninsulated snare wires connected by an electrically-insulating connector to form a snaring loop. The opposing snare wires form the bipolar electrodes of the instrument. The electrically-insulating connector isolates the opposing snare wires so that an alternating electric potential can be applied across the electrodes of the snare loop.
Each of the above-described bipolar snare instruments, suffers from one or more drawbacks associated with the use of the electrically-insulating connector to isolate the ends of the opposing Snare wires. Assembling the ends of the opposing snare wires with the electrically insulating connector adds to the complexity of the manufacturing process, since the connector must be made of an electrically-insulating material such as a plastic, ceramic, glass or epoxy-based material.
The electrically-insulating connector must form a sufficiently strong bond to the snare wires to support the loads generated during surgery. This strength requirement of the connector may also add to the complexity of the snare design. For example, Treat U.S. Pat. No. 4,493,320 describes electrically-insulating connectors having V-shaped, solid rectangular and circular-shaped forms, wherein the ends of the snare wires are imbedded in the connector.
If the bond between snare wires and the insulating connector is not capable of supporting the tensile stresses evolved during actuation of the snaring loop, the instrument may malfunction during surgery. In an extreme case, the connector may become detached from both snare wires and thus detach from the snaring instrument altogether. In endoscopic surgery, such a malfunction may have serious consequences, as it may be extremely difficult to remotely retrieve the detached connector. Additionally, should detachment of the connector go unnoticed until after surgery has been completed, the patient may require additional treatment.
A further drawback of previously known bipolar snare instruments is the need to uniformly withdraw and extend the opposing snare wires when operating the instrument. For effective selective necrosis and hemostasis of tissue, it is desirable that the lengths of the bipolar electrodes be equal throughout the range of actuation of the instrument. Some previously known bipolar snares permit the snare wires forming the electrodes to be withdrawn preferentially from side-to-side or cocked, so that the lengths of the exposed electrodes become unequal. Consequently, the selective necrosis and hemostasis achieved in such cases may be less than that desired to accomplish the objective of the surgery.
In light of the above, it would be desirable to provide an improved bipolar snare instrument for use in surgery that overcomes the drawbacks of previously known snares.
It would also be desirable to provide a snare instrument for use in surgery that does not have the design and manufacturing complexity associated with the electrically-insulating connector of previously known bipolar snare instruments.
It would further be desirable to provide a snare instrument for use in surgery that reduces the likelihood that a component of the instrument will be deposited in the internal tissue regions of a patient during surgery should a malfunction occur.
It would still further be desirable to provide a bipolar snare instrument that promotes effective selective necrosis and hemostasis of tissue by providing uniformly equal lengths of bipolar electrodes during all phases of operation, and which reduces the potential for ineffective necrosis and hemostasis caused by preferential cocking of the opposing snare wires.